Question

这很简单，但我似乎无法找到问题。新元素没有添加到数据库中，我的代码中没有出现任何错误。

这是添加方法

- (void) addPressed:(NSNotification *) message
{
// Insert a new record in the database
Track *track2 = [NSEntityDescription insertNewObjectForEntityForName: @"Track" inManagedObjectContext: managedObjectContext];

[managedObjectContext save: &error];

tracks = [self fetchTracks];


// Insert a new item in the table's data source
[tracks insertObject: track2  atIndex: 0];

// Insert a new row in the table
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection: 0]; 

addTrack.track = [tracks objectAtIndex: indexPath.row]; 

NSLog(@"here");

[[NSNotificationCenter defaultCenter] postNotificationName:@"choosePressed" object:self];


}

调用add后，它会向另一个视图控制器发送一条消息，用户从mpmediapicker中选择一首歌，然后点击一个选择此方法的保存按钮

- (void) finishedEditing 
{


if(start.text.length == 0)
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Warning" message: @"You must fill out all fields" delegate: self cancelButtonTitle: @"OK" otherButtonTitles: nil];
    alert.tag = 1;
    [alert show];
    [alert release];
}
else if(duration.text.length == 0) 
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Warning" message: @"You must fill out all fields" delegate: self cancelButtonTitle: @"OK" otherButtonTitles: nil];
    alert.tag = 1;
    [alert show];
    [alert release];
}
else if(name.text.length == 0) 
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Warning" message: @"You must fill out all fields" delegate: self cancelButtonTitle: @"OK" otherButtonTitles: nil];
    alert.tag = 1;
    [alert show];
    [alert release];
}
else if(songLabel.text.length == 0) 
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle: @"Warning" message: @"You must select a song" delegate: self cancelButtonTitle: @"OK" otherButtonTitles: nil];
    alert.tag = 1;
    [alert show];
    [alert release];
}    
else 
{
    if (repeat) 
    {
        track.title = NULL;
        track.name = NULL;
        repeat = NO;

    }
    else
    {
        songLabel.text = @"";
        artistLabel.text = @"";  
        [self viewWillDisappear: YES];
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil]; 
        track.name = name.text; 
        track.duration = duration.text;
        track.startloc = start.text;
        track.title = [song valueForProperty:MPMediaItemPropertyTitle];
        NSManagedObjectContext *context = track.managedObjectContext; 
        NSError *error = nil; 
        [context save: &error];

        [[NSNotificationCenter defaultCenter] postNotificationName:@"myTraxsTab" object:self];

    }


}

}

我使用NSFetchRequest而不是fetchedResults控制器。这是代码。

request = [[NSFetchRequest alloc] init]; 
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey: @"name" ascending: YES]; 
sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; 
request.sortDescriptors = sortDescriptors; 
[sortDescriptor release]; 
error = nil; 
entity = [NSEntityDescription entityForName: @"Track" inManagedObjectContext: managedObjectContext]; 
request.entity = entity;

更新

好的，所以我在这里的else语句中添加了一行来打印数组

else
    {
        songLabel.text = @"";
        artistLabel.text = @"";  
        [self viewWillDisappear: YES];
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil]; 
        track.name = name.text; 
        track.duration = duration.text;
        track.startloc = start.text;
        track.title = [song valueForProperty:MPMediaItemPropertyTitle];
        NSManagedObjectContext *context = track.managedObjectContext; 
        NSError *error = nil; 
        [context save: &error];

        NSLog(@"array: %@", tracks);

        [[NSNotificationCenter defaultCenter] postNotificationName:@"myTraxsTab" object:self];

    }

这就是它的印刷品。我不知道我失踪了什么。它让我发疯。我显然在名称，持续时间和开始标签上添加了值。

array: (
"<Track: 0x136d80> (entity: Track; id: 0x13a120 <x-coredata://9D789618-64C1-40BF-9F15-BA6A3EA715D3/Track/p7> ; data: {\n    duration = nil;\n    name = nil;\n    startloc = nil;\n    title = nil;\n})"
)

Answer 1

如果你没有任何 ~~crush~~ 崩溃（不仅仅是在这种情况下），首先我会替换字符串：

[managedObjectContext save: &error];

有类似的东西：

// Save the managed object context.
NSError *error = nil;
if (![self.managedObjectContext save:&error]) {
    NSLog(@"Failed to save object to managed object context: %@, %@", error, [error userInfo]);
}

也许（我认为最有可能），在这种情况下，NSlog会给你一些信息。在任何情况下，男人，拯救是一个非常危险的操作，你不应该离开它没有额外的，至少是小的检查。

祝你好运！

修改
你能否发布实际如何从数据库中获取对象？据我了解，你在这里执行：

tracks = [self fetchTracks];

但是那里有什么？另外，我觉得有点混乱：

我使用NSFetchRequest而不是fetchedResults控制器。

您创建一个NSFetchRequest对象，以便描述，您要从数据库中检索（获取）的内容。你做得很好，但我没有在代码中看到你实际使用这个请求然后...
出于检索的目的，正在使用NSFetchedResultsController 。你把它设置为smth。像：

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController;

然后，为了执行实际的提取，你会做一些事情。像：

if (![self.fetchedResultsController performFetch:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); }

（之后你可以从fetchedResultsController获取所有对象）

OR ，如果您不想使用控制器，请直接获取数组：

NSError *error = nil; NSArray *array = [managedObjectContext executeFetchRequest:request error:&error]; if (array == nil) { // Deal with error... }

iPhone - 添加时的核心数据问题

1 个答案: